The present invention relates to a copper alloy sputtering target capable of forming a semiconductor element wiring material, particularly a stable and uniform seed layer which is free of aggregation during copper electroplating, and which has superior sputter deposition properties.
Conventionally, while Al (specific resistance of roughly 3.1 μΩ·cm) has been used as the wiring material of semiconductor devices, pursuant to the miniaturization of wirings, a copper wiring with lower resistance (specific resistance of roughly 1.7 μΩ·cm) has been put into practical application. As the process for forming a copper wiring, generally adopted is the method of forming a diffusion barrier layer made of Ta or TaN on a wiring or a wiring groove, and thereafter electroplating the copper. As the underlayer (seed layer) for performing the electroplating, copper or copper alloy is generally subject to sputter deposition. Conventionally, high purity copper having a purity of 5N to 6N has been produced by performing wet or dry purification to electrolytic copper having a purity level of 4N (excluding gas components) as the crude metal, and this has been used as a sputtering target.
Nevertheless, with a fine wiring in which the copper wiring width is 0.13 μm or less; for instance, 90 nm or 65 nm, and the aspect ratio exceeds 8, the result will be an ultra-thin film in which the thickness of the seed layer is 100 nm or less. When a seed layer is formed using a copper target having a purity of 6N, there is a problem in that aggregation would occur and it is not possible to form a favorable seed layer. Accordingly, it is important to form a uniform underlayer, and when the underlayer becomes aggregated, it is not possible to form a uniform film upon forming a copper film via electroplating. For example, defects such as voids, hillocks, and disconnections are formed in the wiring. Moreover, even if the foregoing defects such as voids are eliminated, since a non-uniform electrodeposited copper structure will be formed at that location, and there is a problem in that the electro migration (EM) resistance will deteriorate. In order to resolve the foregoing problem, it is important to form a stable and uniform seed layer during the copper electroplating, and required is a sputtering target that is optimal for forming a seed layer with superior sputter deposition properties.
Previously, the Applicant proposed a copper alloy sputtering target for forming a semiconductor element wiring, wherein, by adding an appropriate amount of metal elements, the copper alloy sputtering target is able to prevent the generation of defects such as voids, hillocks, and disconnections during copper electroplating, have low specific resistance, and yield electro migration resistance and oxidation resistance (refer to Patent Document 1 and Patent Document 2). While these Patent Documents are able to improve the EM resistance and oxidation resistance since the low resistance properties of copper are not impaired, there was a problem in that a sufficiently uniform film could not be obtained relative to copper wirings which are becoming even finer in recent years.
Note that, while not directly related to the present application, known is a technique of forming a thin film wiring of a semiconductor device by using a copper alloy sputtering target in which various metal elements are added in trace amounts and in which the oxygen content is additionally adjusted (refer to Patent Documents 3 to 5). Nevertheless, none of the foregoing techniques were able to obtain a copper alloy target capable of forming a film having superior uniformity and suitable for semiconductor element wirings which are becoming even finer in recent years.